The present invention relates to a method for compensating static positioning errors, in particular position and orientation errors, in guiding a movement of a movable machine element of an industrial processing machine, such as a numerically controlled machine tool, a robot or the like, with a preset standard parameter for generating reference variables for one or more drives that control the machine elements in a predetermined workspace.
The construction of industrial processing machines requires, among other things, that the machine elements are precisely positioned in order to guarantee today's requirements for accuracy of, for example, workpieces that are to be manufactured with a numerically controlled machine tool.
One characteristic of actual machine tools and robots, in the following referred to as “machines”, is their “absolute positioning accuracy.” This accuracy is expressed in micrometers and degrees, respectively. Their required scale depends on the specific application. In the following, the two terms position and orientation errors are combined into a single term “positioning error.” The positioning accuracy is weighted, among others, by:                Changes in the temperature on the machine and its environment        Gravitational forces on the tool holder        Deformation and wear of the machine elements        Spindle pitch errors in linear axes with ball screws        Sagging of the guide rails, for example caused by the weight of the tool and spindle of the machine tool        Twisting and insufficient straightness of guide rails        Angular errors between the guide rails        Missing information about actual, geometric dimensions of components; frequently, dimensions from the drawings are used instead of the correct information        With non-Cartesian machine tools and robots, the coordinate transformation of the controller is frequently based on only a simplified mathematical model in order to limit the computing time and keep the number of geometric parameters manageable.        
Frequently, the positioning accuracy and in rare cases also the orientation accuracy is measured in the workspace after startup of a processing machine, using external measurement tools. Depending on the application, these values may not be sufficient for the reasons discussed above.
Certain methods have been established to compensate for the underlying causes spindle pitch error and sagging. Twisting and angular error can be compensated by defining narrow tolerances in the machine design. However, the complexity and expenses increase exponentially with the required accuracy, making the processing machine itself also more expensive.
The two latter sources for errors are frequently accepted; alternatively, improvements can be achieved by refining the mathematical model, which however increases the complexity of the software implementation and the required computer resources.
It would therefore be desirable and advantageous to provide an improved method to obviate prior art shortcomings and to decrease static positioning inaccuracies of machines.